Method for treating coal and the like



April 28, 1953 A. D. SINGH 2,536,688

METHOD FOR TREATING COAL AND THE LIKE Filed Feb. 20, 1948 33 35 I fig. Z

ALAMJIT D'. SINGH Patented Apr. 28, 1953 METHOD i-Fon TREATING COALANBLTHE LIKE Alarnjit D. ="-Singh-,- Chicago, 111., assignor to In- Hstitute of -Gas 'llechnology, ()hicago, 11].; a corporationaofslllin'ois-1:

Application February 20, 1948, Serial Noi 9,717;

Thisiinvention relates'to a method for-prepare. ingy frorn coarselyfragmented, coal; 9, hot suspen sion iinqair' of finely comminuted"coal: The: invention also pertains toapparatus adapted forcarrying out"this "and other-methods oftreating" coal.

Reference is made" to" the copending' application of" John I."Ye110tt'SIi8,1T N0. 762,589,*now- Patent? No: 2,515,541; entitledComminution Device-file'd July 22319471 This-ccpending appli-cation-'discloses-a:combination, with a flash pulverizinadevice forsolid material capable of yielding an entrainment-of comminuted solidsin a streaming gasyofra vortex chamber arranged so asito receivesaidstreaming entrainmentina generally tangcntiardirection and at one side"ofithe axis of-said c'hambem-thelatterbeing pro vided' Witlra centralaxial dischargeaperture. thisI apparatus, "coal may be =c0mminuted by amethoddescribed asfollows: The flash pulverizing device includes asource-0f expansible fluid 1 heldunder a pressuresuch-thatthefluid canbe expanded-with'a pressure drop of at-least, l5 lhx per sqxinr- Thecompressedfluid is continuouslydischarged from this source into anelongated conduit, to form a *str'eam'oi' 'compressed flu'id flowing ata velocity less -than one-half l of the critical =velocitybut, inany'event; at least suiii cient tosuspend -therein agranular solidpermeable to the compressed fluid: There is thus" established a streammicompressednuid'fioWin'g in an elongated conduit and capable' otbeing eX-w panded with a pressure drop of at least- 151191"- per sqe ini Thisstreamnof fluid 'is nassedintoa restrictedarea, such as-*a convergentnozzle or a restricted orificegesoa as practically "instant/anew a ouslytot'acoelerate said 'fiuid to -criticals telocity' and simultaneously to-redube the fluidi pressure by R9117: ieast lS lb? per 'sq-s in. Thefluid --is dis charged from the restricted area- (the coiwergrent lnozale unrestricted ormula) as by allowing' the fluid -to escape -into adiver-gent mozzle, into a conduit of iat' least the :samedieimeter :asthe. conduit: tupstrearrrgiciotmEthe; restricted;c area', L or idirectly into ithewortexcchamben Concurrently"a andi continuously,solidagranulesza. reintroduced i into: tlIEifi-OWHIE .str eammf:compress ed: fiuidi su' ciently: faranpstreamsofc. the; constricted: 1area to, suspend: the sand: granules: in the; riot/"ins streamofocompressedfiuidandtoipermitiacceleraticnn said granulesbyisaidstreamin fiuidwingsaid c;- striatedv area .Theiamountof\.- so1idmaterial. troduced intoflthe; streaming fluiduis limitedsso-sp as topermit a pressureydnOp, fat; the restricted areamot.attleastml5tlbapercsq, in In -general, 6 P94113151 y W ght). l ofS0lidsshould bets- 3 Claims. (Cl. 241-'--1) 2 used to each 'partoffluid. Then; -on-passing f through and past therestricted area;'thesolid? granules are shattered, probably "due to thesud den expansion ofthe compressed-fluid contained-" within the granules-Which are permeableto the-- compressed fluid and are believed to-hav'e becomepermeatedthereby while being contacted syme compressed fluid upstream'oftherestricted-area? Thus, the flash pulverizing device'yields a gas-'eous entrainment of comminuted solid particles moving rapidly butunderlower pressure-than the original gaseous entrainment ofrelativelycoarse particles to be commin'uted'." The kinet-ic'energygcontent of the gaseous entrainmentoi' 'comminuted or shatteredparticlesis utilized iorfurther comminutionin the vortex chambrrThe-gas-y eous entrainment of "comminuted 'or shattered particles isdischarged, from the flash pulverizin'g device, through a divergentnozzle; or" through a short conduit (mentioned hereinabove) or,preferably, directly; intothe vortex chamber." This discharge isdirected "generally tangentially inten the vortex chamber, so that therapidly flowing-" gaseous entrainment initially im-pin'ges against thechamber wall and then establishes a vertical or whirling flowinsaid'cham'ber; "which is pro vided with an axial central dischargeopenin'gi-i Due to' the vertical or whirling movement of-thew fluid, therelatively less'fine shattered isarticlesw= move (radially outwardlyWithin the vortex -'cham*--* her, while the relatively fine particlestend-toremain in the central region of thevortex chamber and aredischarged through the central hxial aperture. The relatively less fineparticlesthrewn radially outwardly. Withinthe chamber by contrifu'galforce arewcarriedraround in the oute'r portion of the chamberand"are-theredurthencomminuted by impact against the peripheraw Wall ofthe chamber and with other particle's-and by abrasion between saicl'outer wall and-others particles. When thuscommin'uted;disintegrated orWorn down to smaller particle size,-'the' result-# ing smallerparticles: are discharged through an axial central discharge apertureThus, in the vortexchamber; 'theikineticienergy d of the mixture of afluid andsolids'issuing from the constricted area in thefiashpuiverizingcomw duit is utilized for-further,comminutioneinrth evortex chamber directly v receiving-said.-mixturec.v as low impactagainstthe -walls:ofwdzhei-ivortexw chamber, and by abrasion,againsta-the :wallsqofi-f the vortex chamber.v Further, the-vortex:,chams ber tends to a separate, :the. yariouslyusized solids-.4particles and to pulverize, additionallyithe. coarserezr of thoseparticles. by, impact and/or; attritionm The, method, of thee presentinvention relateszg-sparticularly to the combination, with the flashpulverization step, of immediately succeeding impact and/or attritionsteps utilizing the kinetic en rgy of the flash pulverized gas-solidmixture, as applied to the pulverization of coal with air or otheroxygen containing gases. For this purpose, I have provided additionalsteps and features not shown in said copending Yellott applicationwhereby the comminution of coal with air is rendered more efficient, asdisclosed in further detail hereinbelow.

I have found that in the vortex chamber, coal is shattered moreefficiently if maintained above its softenin or fusion temperature.However, if air is utilized in the flash pulverizing device foreifecting comminution of the coal in the nozzle or constricted area ofthe flash pulverizing device, then the coal must be maintained below itssoftening temperature or fusion point while passing the constrictedorifice or other restricted area in the flash pulverizing device, sinceotherwise the nozzle, restricted orifice or other restricted area in theflash pulverizing device will become clo ged by softened, partiallycoked or even partially burned coal. I, therefore, introducetangentially into the vortex chamber, air at an elevated temperature andmoving relatively rapidly, by means of a conduit dischargingtangentially into the vortex chamber and connected to a suitable sourceof compressed hot air. The hot air thus tangentially introduced into thevortex chamber not only raises the temperature of the flash pulverizedcoal at least to its softening point, but also reinforces andaccelerates the vortical movement within the vortex chamber, to effectimproved comminution within the vortex chamber as well as improvedclassification as between relatively coarse and relatively fineparticles.

It should be understood that the effect of the additional hot airintroduced into the vortex chamber is two-fold. First, due to the rapidflow of the tangentially introduced air, improved separation ofrelatively coarse and relatively fine particles will be effected withinthe vortex chamber, the residence time for the relatively coarseparticles may be prolonged, and, due to the greater gas-solid ratioprevailing in the vortex chamber, a relatively larger amount of kineticenergy is available for comminution of the solids, so that therelatively coarse particles are further comminuted.

Secondly, the mere raising of the temperature of the coal particleswithin the vortex chamber renders the coal more friable, with resultantimproved comminution. In this connection, it should be noted that evenrelatively slight devolatilization (vaporization and separation from thecoal of volatile constituents thereof) may cause the conversion of thecoal particles into gaseous irregular globules with very thin wallswhich pulverize readily, Since the temperature of the coal particles israised very rapidly or practically instantaneously, the gas generatedWithin the coal particles may even cause explosive shattering thereof.

The temperature within the vortex chamber may be maintained by simplypreheating the secondary air or other oxygen containing air introducedinto the vortex chamber to a sumciently high temperature, Withouteffecting cornbustion Within the vortex chamber. In this case, the heatcontent of the secondary air is utilized to maintain the desiredtemperature in the vortex chamber. It is also possible to bring aboutcombustion in the vortex chamber, by suitable regulation of the amountand temperature of secondary air or other oxygen containing gas enteringthe vortex chamber. In this case, the combustion may involve the gaseousproducts evolved from the coal particles in the vortex chamber, so alsothe coal particles themselves, before or after a more or less completedevolatilization. Where relatively high temperatures are desired, Iprefer to bring about partial combustion within the vortex chamber.Particularly good comminution is effected at 1100 F. or highertemperatures.

The product of the instant process is a hot suspension in air of finelycomminuted more or less incompletely devolatilized coal. The heatcontent of the suspension may be utilized by subjecting the hotsuspension to combustion, to gas forming reactions, or to other chemicalprocesses wherein the heat content of the suspension is utilized. Inother words, the product of the instant process may be considered asbeing a preheated mixture of air and finely comminuted, more or lessdevolatilized coal suitable for use in other and further processes.

The apparatus of the present invention differs principally from thatdisclosed and claimed in said copending Yellott application by theprovision of a tangential gas inlet into the vortex chamber adapted tobe connected to a source of compressed hot air or the like. Obviously,this apparatus may also be employed for the introduction of other gasesinto the vortex chamber.

It is therefore an important object of the present invention to providean improved method for the comminution of coal by means of air or otheroxygen containing gas at a temperature above the softening point of thecoal yielding a hot suspension in air of more or less devolatilized,finely comminuted coal.

Another important object of the present invention is to provide animproved method for comminuting coal involving an initial flashpulverization of the coal with air or other oxygen containing gascarried out below the softening or fusion point of the coal followed byan impact and/or attrition step utilizing the kinetic energy of theflash pulverized air-coal mixture at a temperature above the softeningpoint of the coal reached by addition, to the flash pulverized coalairmixture, of additional air at an elevated temperature.

A further important object of the present invention is to provide animproved comminution device suitable for use in the grinding of coal andcomprising a flash pulverizing device discharging directly andtangentially into a vortex chamber also receiving tangentiallyadditional amounts of a gas such as hot air.

Other and further objects and features of the present invention willbecome apparent from the following description and appended claims takenin conjunction with the accompanying drawings which show,diagrammatically and by way of example, apparatus according to thepresent invention for carrying out the novel and improved processdescribed above. More particularly:

Figure 1 is a vertical cross-sectional view, with parts shown inelevation, of an apparatus according to the present invention; and

Figure 2 is a transverse cross-sectional view taken along the line II-IIof Figure 1.

As shown on the drawings:

In Figure 1, the numeral l0 indicates a hopper hav g a 0 0. 1 bot om forreceiving coarsely Air or otherv oxygen containing gas is admitted intothe system at twolocalities. First, the air required for flashpulverization is admitted into the conduit and there admixed with thecoal. Additional amounts of air are adpreferred temperatures of thesetwo sources of air are discussed in the following paragraphs.

The temperature of the air flowing through the conduit should be suchthat no clogging of the nozzle 25 will take place, i. e., neither thefusion nor the combustion temperatures of the coal should be reached.This end will be attained if the temperature of the air admitted intothe conduit 20 is kept below 600 F. and, preferably, not higher than 500F. The exact maximum permissible temperature at the nozzle 25 and in theconduit 20 is determined by the fusion point of the coal, which variesaccording to the origin of the coal. By way of example, I tabulatehereinbelow the values obtained by the United States Bureau of Mines inthe determination of the softening temperatures of nine samples of coalobtained from different localities:

These figures have been taken from Table 1', United States Buerau ofMines, Monograph 1934.

While the temperature in the conduit 20 and in the nozzle 25 should bemaintained below the softening temperature of the coal being comminuted,the temperature in the vortex chamber should be maintained above thesoftening temperature of the coal. The heat required for this purposemay be derived exclusively from the hot air introduced into the vortexchamber 30 through the conduit 35, or may be derived partially from theheat content of this air and partially from. an incomplete combustion ofthe coal or products of devolatilization of the coal effected within thevortex chamber 30. Whether or not such incomplete combustion will occurde pends, of course, upon whether or not the ignition temperature of thecoal or products of devolatilization of the coal is reached within thevortex chamber 30. Partial combustion within the Vortex chamber 30brings about a relatively high temperature with resultant finercomminution, as compared to the case when the temperature isinsufiicient for combustion within the vortex chamber, although, in thelatter case. the

comminution is finer than when the temperature in the vortex chamber 30falls below the softening temperature of the coal.

Combustion within the vortex chamber .30 is initiated and maintained bythe fiow of hot air or other oxygen containing gas through the con-TABLE I Experimental data on the flash pulueriaation of Illinois coalRatio Ratio Temp 'Iem Temp. Center p Exp. N o. PXEHQW Suppl PrimaryVortex SUPP! 1r to Air to Air 0 F Cha b An, Coal Coal 0%. O r.

1. 3e 2. 7 500 580 1, 300 0. s4 2. 0 450 730 1, 650 0.217 1. 2 330 4801, 185 1. 23 1. 2 450 1, 400 1, 575 1. 10 2. s 320 1, 700 1,380 1. 142.0 360 1, 330 1, 160 1. 29 2. 3 310 1, 380 1, 310

TABLE II Analytical data on the flash puloerization of Illinois coalScreen Analysis-Percent Retained on U. S. Volatile Sieve Exp. No.Matter, Percent 20 10 so 200 32s -:s25

31. 0 4.8 11.0 13. 6 19. 2 22.0 8.0 21.0 24.9 0.2 1.0 1.8 5.2 12.2 7.671.8 30.8 8. 4 12.0 12. 5 16. 4 18.7 7. 5 23. 7 29. 8 0.7 1.0 3. 0 7. 615. 1 8. 7 63. 0 31. 0 12.3 13.3 11. 7 15.2 17. 7 7. 3 22.0 30. 4 0.5 2.0 3. 6 7. 7 14. 5 8.6 63. 8 31. 2 6. 3 10.0 9. 8 13. 4 16. 7 10.2 31. 715. 2 0.0 1. 2 0.8 1.6 5. 8 8. 1 82. 5 35. 5 0.0 34. 6 22.0 17. 6 l2. 53. 6 10.5 14. 2 0. 8 2. 5 3. 2 9. 2 14. 0 8. 5 61. 0 35. 6 0.0 27.0 22.6 18.9 13.8 4. 0 12.8 32. 0 0.0 0.3 1. 4 5.8 23. 5 15. 5 53. 1 33. 2 0.1 25. 3 20. 7 18. 4 l3. 5 5. 1 15.2 28. 6 0. 4 O. 6 0. 5 2. 9 12. 6 9. 374. 2

F Refers to Feed.

P Refers to Product.

The above'tabulated data were obtained with an upstream air gaugepressure varying from '78 to 86 lb. per sq. in.; a downstream vacuum ofabout 1 in. of mercury; approximately atmospheric supplementary airpressure. In the last four tabulated experiments, combustion occurredwithin the vortex chamber.

"Particular attention is directed'to the fact that the finestcomminuation occurred when combustion took place'within the vortexchamber. Further, the greatest extent of devolatilization occurred whencombustion took place within the vortex chamber, although the fact thatsuch combustion takes place does not necessarily bring about a; highdegree of devolatilization.

It will thus be seen that I have provided a novel method fordisintegrating coal by the use of compressed air at an elevatedtemperature including the steps of (l) forming a suspension of coarselycomminuted coal in air or other oxygen containing gas belowthe'soitening temperature of the coal but, preferably, within 100 to200- F. within said softenin temperatur said acsaese 11 pension within acylindrical axially limited space while forming said suspension into avortex, the rate of flow within said vortex bein such that saidshattered particles are kept circulating within said space and therebyfurther comminuted, and withdrawing from the center I of said vortex gashaving suspended therein relatively fine coal particles, the improvementcomprising maintaining the temperature of said coal upstream of saiddischarge point below the softening point but within 200 F. of saidsoftening point, incorporating additional gas containing free oxygenwith said vortex at substantially the same pressure as that prevailinginside said vortex, and eiiecting combustion in said vortex to maintainthe temperature thereof at from 800 to 1800 F.

3. In the method of disintegrating granular coal which comprisesproviding a source of compressed gas capable of being expanded with apressure drop of at least 15 pounds per square inch, continuously anduninterruptedly discharging gas from said source while confining thedischarged gas to establish a stream of gas flowing uninterruptedly andcontinuously from said source to and past a discharge point spaced fromsaid source, concurrently, continuously and uninterruptedly introducingsaid coal into said stream ahead of said discharge point foracceleration and suspension of the coal granules by said gas ahead ofsaid discharge point, at said discharge point establishing andcontinuously and uninterruptedly maintaining a sharp gas pressuregradient, the pressure of said granule suspending gas beinginstantaneously reduced as said granule suspending gas continuously anduninterruptedly flows past said discharge point, said stream of gashaving a substantially uniform cross sectional area upstream of saiddischarge point and being sharply constricted only at said dischargepoint whereby the total gas pressure drop in said stream is concentratedat said discharge point, the drop in gas pressure at said dischargepoint being continuously and uninterruptedly maintained at a value of atleast 15 pounds per square inch and the gas pressure immediatelydownstream of said discharge point being reduced at least to an extentwhere further downstream pressure reduction will not bring about asubstantially increased weight rate of flow past said discharge point,said coal being introduced into said stream in the form of granulessmaller than the cross section of said stream at said discharge point 12and in an amount not greater than six parts by weight of coal for eachpart by weight of gas, each of said suspended coal granules beingcarried in suspension by said streaming gas along a substantiallystraight path to and past this discharge point and there furtheraccelerated and subjected to said instantaneous drop in gas pressurewhereby all said coal granules are disintegrated in the same manner andthere is formed a rapidly flowing suspension of shattered coal particlesin expanded gas, confining said rapidly flowing suspension within acylindrical axially limited space while forming said suspension into avortex, the rate of flow within said vortex being such that saidshattered particles are kept circulating within saidspace and therebyfurther comminuted, and withdrawing from the center of said vortex gashaving suspended therein relatively fine coal particles, the improvementcomprising maintaining the temperature of said coal below the softeningpoint upstream of said discharge point, incorporating additional gascontaining free oxygen with said vortex at a pressure substantially thesame as that prevailing inside said vortex and effecting combustion insaid vortex to maintain the temperature thereof above the softeningpoint of said coal, said combustion being initiated by heating saidadditional gas before said additional gas is incorporated with saidvortex.

ALAMJIT D. SINGH.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 369,836 Blackman Sept. 13, 1887 1,578,609 Mason Mar. 30, 19261,922,313 Mason Aug. 15, 1933 2,032,827 Andrews Mar. 3, 1936 2,184,300Hodson Dec. 26, 1939 2,306,462 Moorman .1 Dec. 29, 1942 2,385,508Hammond Sept. 25, 1945 2,392,866 Stephanoff Jan. 15, 1946 2,515,541Yellott July 18, 1950 2,515,542 Yellott July 18, 1950 OTHER REFERENCESReport of Investigation R. I. 3306, pages 8, 9 and 10, 1936.

Article, D. Meigs in February 1941 issue, of Chemical and MetallurgicalEngineering (pp. 122-125).

Industrial and Engineering Chemistry for July 1946, pages 672-678.

